1. Field of the Invention
The invention relates to compositions comprising at least one monomer component incorporated into an aqueous polymer dispersion by swelling the polymer component of the dispersion, and to a composition comprising initiators and activators. Following the evaporation of the aqueous phase, the monomer/polymer composition forms a film and the polymerization of the monomer component is initiated. The result is a clear, compatible film having a new polymer phase formed by the polymerization of the monomer in the existing polymer phase.
2. Discussion of the Background
Hydrophobic binders tend to emit volatile monomers, thus causing potential environmental, health, safety, and odor problems. The conventional solution to this problem is to replace a portion of the methyl methacrylate monomer component of such compositions with relatively high-boiling monomers, such as butyl methacrylate. However, the amount of butyl methacrylate cannot be raised to too high a level, because, for example, the resulting polymers would be too soft (see, for example, DE 198 26 412). In addition, substituting less volatile monomers (e.g., butyl methacrylate) for volatile monomers (e.g., methyl methacrylate) only partly solves the emission problem because low molecular weight monomers, such as methyl methacrylate, are still present, and are still emitted at measurable levels.
The object of the present invention, therefore, is to develop a monomer/polymer composition which has good mechanical properties and emits very little, if any, monomer. Moreover, the composition should be easy to handle and should possess a high level of storage stability.
Accordingly, it is an object of the present invention to provide a monomer/polymer composition comprising two components A and B, or a mixture thereof, wherein component A comprises:
a) an first emulsion polymer formed from 1-99% by weight of a C1-C10 alkyl acrylate, 99-1% by weight of C1-C10 alkyl methacrylate, and 0-0.5% by weight of a graft component chemically incorporated into the first emulsion polymer;
b) at least one first ethylenically unsaturated monomer incorporated into the first emulsion polymer; and
c) a polymerization initiator dissolved in the first ethylenically unsaturated monomer;
component B comprises:
d) a second emulsion polymer formed from 1-99% by weight of C1-C10 alkyl acrylate, 99-1% by weight of C1-C10 alkyl methacrylate, and 0-0.5% by weight of a graft component incorporated chemically into the second emulsion polymer;
e) at least one second ethylenically unsaturated monomer incorporated into the second emulsion polymer; and
f) a polymerization activator dissolved in the second ethylenically unsaturated monomer;
wherein the first and second emulsion polymers are swollen with, respectively, the first and second ethylenically unsaturated monomers.
Component A comprises a first aqueous emulsion polymer formed from:
1. 1-99% by weight, based on the polymer, of C1-C10 alkyl methacrylates,
2. 99-1% by weight, based on the polymer, of C1-C10 alkyl acrylates,
3. 0-0.5% by weight, based on the polymer, of a first graft component, incorporated chemically in the first emulsion polymer.
4. At least one first ethylenically unsaturated monomer.
The first ethylenically unsaturated monomer of component A contains 0.1-5% by weight, based on the amount of first ethylenically unsaturated monomer, of at least one polymerization initiator, for example a peroxide. The amount of first ethylenically unsaturated monomer of component A may be from 1% by weight to 50% by weight, based on the amount of emulsion polymer.
Component B comprises a second aqueous emulsion polymer formed from:
1. 1-99% by weight, based on the polymer, of C1-C10 alkyl methacrylates,
2. 99-1% by weight, based on the polymer, of C1-C10 alkyl acrylates, the solids content of the dispersion being between 30% by weight and 60% by weight,
3. 0-0.5% by weight, based on the polymer, of a second graft component, incorporated chemically in the second emulsion polymer.
4. At least one second ethylenically unsaturated monomer.
The second monomer of component B contains 0.1-5% by weight, based on the amount of ethylenically unsaturated monomer, of at least one amine activator or at least one activator based, for example, on vanadium. The amount of second ethylenically unsaturated monomer of component B is 1-50% by weight, based on the amount of the second emulsion polymer.
The solids content of the dispersions A and B is between 30 and 60% by weight.
The C1-C10 alkyl methacrylates of which the first and second emulsion polymer are comprised may be esters of methacrylic acid, such as methyl methacrylate, ethyl methacrylate, propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, tert-butyl methacrylate, pentyl methacrylate, hexyl methacrylate, heptyl methacrylate, octyl methacrylate, isooctyl methacrylate, ethylhexyl methacrylate; and also cycloalkyl methacrylates, such as cyclohexyl methacrylate or tetrahydrofurfuryl methacrylate, isobornyl methacrylate.
The C1-C10 alkyl acrylates of which the first and second emulsion polymer are comprised may be esters of acrylic acid, such as methyl acrylate, ethyl acrylate, propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, tert-butyl acrylate, pentyl acrylate, hexyl acrylate, heptyl acrylate, octyl acrylate, isooctyl acrylate and ethylhexyl acrylate; and also cycloalkyl acrylates, such as cyclohexyl acrylate.
The first and second ethylenically unsaturated monomers may comprise, for example, any of the following, including mixtures thereof:
C1-C10 alkyl methacrylates, as defined above;
hydroxy esters of methacrylic acid, such as 2-hydroxyethyl methacrylate, hydroxypropyl methacrylate; and
ether esters, such as 2-(2-(2-ethoxyethoxy)ethoxy)ethyl methacrylate and 2-(2-butoxyethoxy)ethyl methacrylate.
The first and second ethylenically unsaturated monomers may each comprise 1%-50%, preferably 10%-20%, based on the amount of polymer in the respective dispersions of component A and component B, and may be the same or different. The ethylenically unsaturated monomers are incorporated into the polymer dispersion by allowing the monomer to swell the polymer. By swelling the polymer, we mean that the ethylenically unsaturated monomer penetrates into the polymer particles of the dispersion, without actually dissolving the polymer particles. Thus, the ethylenically unsaturated monomer is dispersed, on a molecular level, in the polymer phase of the polymer dispersion.
The optional first and second graft component of the respective emulsion polymers may be a comonomer containing, for example, allyl groups, hydroxyl groups or mercapto groups, et cetera.
In addition, 0-5% by weight of an optional crosslinker or mixture of crosslinkers may be added to either or both of component A and component B. Such crosslinkers may include, for example, 1,4-butanediol dimethacrylate, tetraethylene glycol dimethacrylate, triethylene glycol dimethacrylate, trimethylolpropane triacrylate and trimethylolpropane trimethacrylate.
Examples of suitable peroxides for component A may include, for example, organic peroxides such as dibenzoyl peroxide and dilauroyl peroxide.
Component B may have the same or different composition as component A, except that instead of a peroxide, component B has an amine, such as N,N-dimethyl-p-toluidine, N,N-bis(2-hydroxyethyl)-p-toluidine or N,N-bis(2-hydroxypropyl)-p-toluidine, for example. The peroxide of component A and the amine of component B form a redox composition when components A and B are mixed, which may be used as a polymerization initiator. As an alternative to the above-mentioned peroxide/amine redox composition a hydroperoxide/vanadium activator polymerization initiator may be used.
Suitable hydroperoxides may include, for example, tert-butylhydroperoxide, cumene hydroperoxide, and ketone peroxides. Ketone peroxides may include, for example, methyl ethyl ketone peroxide, methyl isobutyl ketone peroxide or cyclohexanone peroxide, individually or as a mixture. Vanadium activators may include, for example, acidic vanadium phosphates in combination with coactivators, such as lactic acid.
Components A and B may have virtually unlimited storage stability and may be stored separately or as a mixture of the two components. Monomer/polymer compositions of the present invention may also be prepared by adding the activator of component B, in aqueous solution, to an initial charge of component A, or by adding the peroxide of component A, in aqueous solution, to an initial charge of component B.
Having generally described this invention, a further understanding can be obtained by reference to certain specific examples which are provided herein for purposes of illustration only, and are not intended to be limiting unless otherwise specified.